Alligator clip adapted for smaller plug

ABSTRACT

An alligator clip ( 10 ) whose rear end was originally manufactured to receive a 4 mm plug ( 50 ), is altered to received a 2 mm plug ( 60 ), in a construction that provides a long lifetime of low force insertion and removal and low electrical resistance contact. The sheet metal rear portion with adjacent edges ( 40, 42 ) at the top, is deformed so a bottom part forms an approximately 360° loop ( 130 ), a pair of vertical bottom beams ( 131, 132 ) extending upward from the loop, and a pair of part-cylinders ( 140, 142 ). The part-cylinders create a cylinder contacting region ( 150 ) at the top of the beams to grip the cylindrical 2 mm plug. Upper beams ( 152, 154 ) extend generally upwardly from the upper ends of the part-cylinders.

BACKGROUND OF THE INVENTION

[0001] One type of alligator test clip has a pair of jaws at its front end that are spring biased together, and that has a socket or pin jack at its rear end that is designed to receive a 4 mm diameter plug. The plug may be used alone for insertion into jacks of equipment to be tested, but may be inserted into the pin jack at the rear of the alligator clip to clamp to a wire. Although the 4 mm plug is the most common in present use, there are significant numbers of 2 mm diameter plugs, and there is a need for alligator clips whose rear ends can receive such 2 mm plugs.

[0002] The alligator clip includes two pieces of sheet metal and a spring, with a first of the pieces having a rear portion bent into a cylinder to form the 4 mm pin jack. The opposite edges of the first piece of sheet metal lie at the top of the cylinder, where the edges are parallel and adjacent. Applicant has previously changed the 4 mm pin jack by compressing opposite sides of the cylinder, to the configuration shown in FIG. 8. While this approach results in a useful 2 mm pin jack, it has serious problems. One problem is that it requires a large force such as twenty pounds to insert and retract the 2 mm plug from the prior pin jack shown in FIG. 8. Also, the electrical resistance was initially significantly higher (about 13 miliohms) then for the 4 mm jack (about 6 miliohms). Also, after perhaps ten or twenty insertions and removals of the 2 mm plug from the prior 2 mm jack, electrical contact was sometimes lost between the jack and plug.

[0003] It is possible to adapt the 4 mm jack to a 2 mm jack by inserting a device with a sleeve and tiny beams, but such contactor adds significantly to the cost. An adaption of the prior 4 mm simple cylindrical jack to a 2 mm jack by merely deforming the jack part of an alligator clip, where the adaption resulted in a 2 mm jack with low insertion and removal force and low electrical contact resistance, with the low insertion and removal forces and low contact resistance continuing over a long cycle of use (numerous insertions and pullouts of the plug) would be of value.

SUMMARY OF THE INVENTION

[0004] In accordance with one embodiment of the present invention, an alligator clip is provided with a pin jack at the rear, where the pin jack has been adapted from a cylindrical large diameter jack to a smaller diameter jack, where the small diameter jack provides for small insertion and removal forces and a low electrical resistance connection to a small plug, over a large number of duty cycles. The clip includes a first piece of sheet metal with a rear portion having a pair of parallel edges at its top. The rear portion has a gripping section extending along an axis, where the gripping section has a bottom part that form an approximately 360° bottom loop and a pair of primarily parallel bottom beams that extend upwardly from opposite sides of the bottom loop. The gripping section also has opposite sides each formed into a continuous part cylinder and that together form a cylinder contacting region that grips the small diameter cylindrical plug. Beams extend at least partially upward from the tops of the part cylinders. The edges of the sheet metal lie at the top of the gripping section and extend parallel to each other.

[0005] The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a rear and top isometric view of a prior art alligator clip for receiving a large diameter jack, and showing a portion of the jack, with the clip of this figure being an item that is deformed to form the clip of the invention.

[0007]FIG. 2 is a top and rear isometric view of a portion of a clip of the present invention for engaging a small diameter plug, and which has been formed from the clip of FIG. 1.

[0008]FIG. 3 is a side elevation view of the clip of FIG. 2.

[0009]FIG. 4 is a bottom view of the clip of FIG. 3.

[0010]FIG. 5 is a rear elevation view of the clip of FIG. 3, taken on line 5-5 thereof.

[0011]FIG. 6 is a sectional view taken perpendicular to the jack horizontal axis and on line 6-6 of FIG. 3.

[0012]FIG. 7 is an enlarged view of the gripping section shown in FIG. 6, and is also taken on line 6-6 of FIG. 3.

[0013]FIG. 8 is a sectional view of a gripping section of a prior art converted clip for engaging a small diameter plug.

[0014]FIG. 9 is an exploded view showing the manner in which the rear portion of the clip of FIG. 1 is deformed into the gripping section of the clip of FIG. 2.

[0015]FIG. 10 is a sectional view of the gripping section of a clip of another embodiment of the invention.

[0016]FIG. 11 is a sectional view of the gripping section of a clip of another embodiment of the invention.

[0017]FIG. 12 is a sectional view of the gripping section of a clip of another embodiment of the invention.

[0018]FIG. 13 is a side elevation view of an alligator clip of another embodiment of the invention.

[0019]FIG. 14 is a view taken on line 14-14 of FIG. 13.

[0020]FIG. 15 is a partial sectional view of the clip of FIG. 13 with a rubber boot.

[0021]FIG. 16 is a view taken on line 16-16 of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022]FIG. 1 illustrates an alligator clip 10 from which the clip of the present invention is made. The alligator clip includes a body 12 that has first and second body parts 14, 16 that are each formed of bent sheet metal, the sheet metal usually being carbon steel which is plated. The two body parts are pivotally connected at a pivot joint 20 to allow front ends 22, 24 of the body parts to move together and grip a wire or other element between them to make electrical connection with the element. A coil spring 26 urges the front ends 22, 24 together. The first part or piece of sheet metal 14 has a rear portion 30 forming a pin jack 32. The pin jack is formed by the rear portion of the first piece 14 of sheet metal, by the sheet metal having been bent into an original cylinder 34 with first and second edges 40, 42 at the upper, in direction U, end or top of the cylinder. The cylinder extends in a continuous circle from edge 40 around the laterally L opposite sides 44, 46 and around the downward D or bottom end 48. In the particular example shown, the large plug 50 that can be received in the pin jack 32, has a front end 52 and shaft 54 that are each of 4 mm diameter.

[0023] Although the alligator clip 10 of FIG. 1 is in wide use, there is a substantial demand for alligator clips that can receive small diameter plugs 60 having tips 62 and shafts 64 that are each of 2 mm diameter. One way to convert the clip 10 to receive and make electrical connection with the small diameter plug 60 is to insert a contacting element in the pin jack 32, where such element has inwardly bowed fingers that engage the small plug 60. However, such insert adds substantial cost to the clip. Another approach is to deform the pin jack 32 so a section of it has the gripping section cross section shown in FIG. 8 at 70. In such clip, the first and second laterally spaced edges 40, 42 of the sheet metal remain at the top, but the laterally opposite sides of the original cylinder are deformed at 44A, 46A into a pair of 360° side loops 80, 82 with horizontally-extending side beams 84, 86, and 90, 92. Also, upper and lower portions 100, 102 of the original cylinder are deformed into approximately half cylinders that form a tubular, or cylinder section 104 having an inside diameter 106 slightly less than 2 mm. The gap 108 between the edges 40, 42 lies in the upper part cylinder portion 100 that grips the plug.

[0024] Although the gripping section 70 of FIG. 8 can receive and connect to a small diameter 2 mm plug, it has disadvantages. Applicant found that, with the carbon steel metal of thickness A of 19 mils (1 mil equals 1 thousandth inch), that the clip required a plug insertion and pullout force for the 2 mm plug, of about twenty pounds. This is a large force for a person to apply to a small jack. While the electrical contact resistance between the large plug 50 of FIG. 1 and the large pin jack 32 was about 5 miliohms, the contact resistance for the 2 mm plug was initially about 13 miliohms. Furthermore, after about ten to twenty insertions and pullouts of the small pin contact from the section 70 of FIG. 8, a plug sometimes lost electrical contact with the gripping section 70 of the jack.

[0025] In accordance with the present invention, applicant deforms the rear portion 30 of FIG. 1 into the configuration shown at 30B in FIG. 2. The alligator clip 120 of the invention shown in FIG. 2, has a tapered leadin 122 at its rear end and a gripping section 124 extending forward F of the leadin. FIG. 3 is a side view of the clip 120 of the invention, showing the manner in which the rear portion 30B of the first piece 14A of sheet metal has been deformed.

[0026]FIG. 7 is a view taken on line 6-6 of FIG. 3 showing the cross section of the gripping section 124 of the alligator clip of the invention. The sheet metal has been deformed to form an approximately 360° bend or circle loop 130 at the bottom of the gripping section. A pair of bottom beams 131, 132 have lower ends 134 that merge with opposite sides of the circle loop 130. The bottom beams 130, 132 extend primarily upwardly, and preferably directly upwardly and parallel to each other, to their upper ends 136. At their upper ends 136, the bottom beams merge with part cylinder portions 140, 142 that are each bent into a portion of a cylinder centered on axis 144. The two part cylinder portions are spaced apart by a distance B which is slightly less than 2 mm, such as 1.95 mm, to grip a plug of nominal 2 mm outside diameter. The two part cylinders 140, 142 together form a cylinder region 150 that is similar to a cylinder of the diameter B to receive and engaged a 2 mm diameter plug. The gripping section has a pair of upper beams 152, 154 that extend upwardly to the edges 40, 42, with the edges being free and unjoined.

[0027] Applicant has found that the alligator clip 120 of the present invention with the gripping section 124 shown in FIG. 7, provides only a moderate mechanical resistance of about two pound to insertion and retraction of a 2 mm plug, provides a low electrical resistance of about 6 miliohms, and maintains a low electrical resistance (Under 10 miliohms) and the moderate mechanical resistance to insertion and retraction throughout numerous cycles of operation. In fact, applicant found that in some tests the low electrical and mechanical resistances were maintained for ten thousand cycles of insertion and retraction.

[0028] For the particular gripping section 124 in FIG. 7, the overall height C of the section was 277 mils (6.86 mm or 0.277 inch), the radius of curvature G at the loop 130 was 25 mils (0.64 mm) and the separation S between lower beams was 15 mils (0.4 mm). The part cylinders 140, 142 each extended by an angle V of about 135° around the axis. 135° is 75% of a half cylinder of 180°. The lengths E and F of the lower and upper beams were 1.9 mm (75 mils). The length E of the lower beams 131, 132 are important in determining the insertion and retraction force, and the lengths F of the upper beams are the result of using all of the sheet metal that is initially present. Referring to FIGS. 3 and 4, the overall length of the clip was 1.96 inch and the leadin 122 had an outside diameter J of 0.19 inch. The distance K between the axis 144 and the bottom of the loop 130 was 0.135 inch, with the bottom of the loop lying a distance P of 0.06 inch (1.5 mm) below the bottom 192 of an intermediate wall. The distance P is more than half the diameter B of the cylindrical plug.

[0029] It is not readily apparent why the cross section of the gripping section 124 of FIG. 7 should provide such lower mechanical force in insertion and retraction and such greater reliability in maintaining low electrical contact resistance with the inserted plug. One reason is that the length of the beams 131, 132 is greater than that of beams 84-92 due to the need for two loops 80, 82 in the prior art. Applicant believes that another reason is that in FIG. 7, the part cylinder portions 140, 142 need to bend apart only one circle loop 130, while in the prior art of FIG. 8, the inserted plug must bend apart two circle loops 80, 82. Applicant also believes that the advantage may be due to the fact that there are only two areas of contact in the gripping section 124 of FIG. 7, at the general locations 170, 172. In the gripping section of FIG. 8, there would be three locations that must be spread apart, including locations on the two parts 101, 103 of the upper half cylinder, and a part on the lower half cylinder 102. Also, applicant believes that there are likely to be burrs or other irregularities at the bottom corners 40E, 42E of the edges 40, 42, and such burrs may scrape along the plug, impede insertion and retraction of the plug, and give rise to irregularity of mechanical and electrical resistance. In any case, applicants' tests on numerous alligator clips of the type shown in FIGS. 2-7 and a comparison with a prior art clip of FIG. 8 shows that applicants' lower and more consistent mechanical and electrical resistance and long lifetime, do in fact, occur.

[0030] In the clip 10 of FIGS. 1 and 2, the first sheet metal part 14 has an intermediate part 190 with a flat bottom 192 that lies in a horizontal plane and with side wall 193, 194 that extend upwardly from laterally opposite sides of the bottom wall. The edges 40, 42 remain above the level of the bottom wall 192 in the clip 120 of FIG. 2. However, the circle loop 130 in FIG. 2 lies below the level of the bottom 192 after the deformation into the gripping section 124. This is clearly shown in FIG. 3 where the bottom of the loop 130 is shown lying below the height of the lower surface 192 of the flat bottom.

[0031]FIG. 9 shows one method for deforming the rear portion 30 of the original clip (for receiving a 4 mm plug) into the gripping section 124 of the clip of the present invention. A pair of dies 180, 182 have surfaces 184, 186 that are pressed against opposite lateral sides of the initial sheet metal rear portion 30. Also, a core 190 is inserted into the rear portion. When the dies are pressed together with high force, the rear potion 30 is deformed into the gripping section 124 which has final sides at 140, 142. The deformation can be accomplished in steps by a series of dies. The bottom 193 of the bottom loop 130 lies below the bottom 48 of the original cylinder 34, which lay slightly (0.03 inch) below the bottom 192 of the intermediate part. The bottom 193 of the bottom loop lies a distance P below the bottom wall, where P is more than twice the thickness of the sheet metal.

[0032]FIG. 10 illustrates a gripping section 200 of another embodiment of the invention, wherein the bottom beams 202, 204 that extend upwardly from an approximately 360° loop 206, are of greater length, and the upper beams 210, 212 are of shorter length. This results in even lower mechanical resistance to insertion and retraction of the plug, but can lead to somewhat greater electrical resistance.

[0033]FIG. 11 shows another gripping section 220, where each of the opposite sides 222, 224 is half of a square shape (or hexagonal or octagonal), but are basically part cylinder portions because they can engage a cylindrical plug 60 at at least three and preferably at least four locations 211 spaced about the axis 144 of the plug. Two concave cylinder parts such as shown in FIG. 10 at 213, 214 engage a cylindrical plug at regions 215, 216 (for a smaller diameter plug) or at locations 217A-217D for a larger diameter plug. This holds the plug centered on the axis 144.

[0034]FIG. 12 illustrate another gripping section, where the bottom circle loop 272 subtends an angle N of 310°, resulting in each bottom beam 274, 276 extending at an incline of 25° from the vertical but still primarily vertical. The part-cylinder portions 280, 282 grip a cylindrical plug 284. The gripping occurs at closely spaced points 290, at each part-cylinder portion for a small diameter plug, and at widely spaced locations such as 294, 296 at each part-cylinder portion for a large diameter plug. Like the other clips, the clip 270 is symmetric about a vertical centerline.

[0035] FIGS. 13-16 illustrate another alligator clip 230 that applicant constructed. This clip is similar to the clip of FIGS. 1-7, but with a greater outside radius of curvature G1 (FIG. 14) of 1 mm and with the lower beams separated a distance S1 of 1.25 mm. This is five times the separation S in FIG. 7 and the separation S in the prior art of FIG. 8, and is more than 150% of the thickness A of 0.019 inch (0.48 mm) of the sheet metal. This results in much less force required to insert the 2 mm plug. The clip has opposite part cylinder portions 232, 234 that each extends by an angle V1 of only about 75°. The upper beams 250, 252 have a height C1 that is about 60% of the height E1 of the lower beams 254, 256.

[0036] FIGS. 15-16 show a rubber boot 240 that applicant uses to surround the clip. The boot isolates the person holding and applying the clip, from any voltage on the clip. The boot has a section 242 shown in FIG. 15, which closely surrounds the gripping section 244 of the clip and which can add resilience to grip the plug.

[0037] While terms such as “upper”, “bottom”, “horizontal”, etc. have been used to help describe the invention as it is illustrated, it should be understood that the clip can be used in any orientation with respect to the Earth.

[0038] Thus, the invention provides an alligator clip with a jack for a small diameter plug, where the jack has a small mechanical resistance to insertion and retraction of the plug and the jack has a low electrical resistance engagement with the plug, and maintains these characteristics over a long lifetime of use. This is achieved where the jack is formed by deforming an existing larger jack. The clip includes a piece of sheet metal with unjoined edges at the top and two laterally spaced approximately half cylinder portions that can grip a plug between them. The sheet metal has been deformed to form an approximately 360° (at least 300°) bottom circle loop at a bottom end that is opposite the edges, and to form a pair of primarily vertically extending bottom beams that each extends from one side of the loop to the bottom of each half cylinder portion. A pair of upper beams extend primarily upwardly from upper ends of each half cylinder portion. A bottom loop of a large radius of curvature that is at least one and one-half or twice the sheet metal thickness, results is easy pin insertion.

[0039] Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents. 

What is claimed is
 1. An alligator clip with a body formed of two pieces of bent sheet metal having front ends and a spring that biases said front ends together, with a first of said pieces of sheet metal having a rear end forming a pin jack, wherein said pin jack includes a gripping section having an axis and having parallel and adjacent sheet metal top edges lying above said axis with said edges unjoined to each other, wherein: along said gripping section of said pin jack, said sheet metal has a bottom portion where said sheet metal forms primarily vertical bottom beams with lower ends joined at a bottom loop, and above said bottom beams said sheet metal forms two continuous part-cylinder portions that each extends from an upper end of one of said bottom beams and with said part-cylinder portions together forming a cylinder region centered on said axis to hold and engage a cylindrical pin.
 2. The alligator clip described in claim 1 wherein: along said gripping section of said pin jack, said sheet metal forms a pair of upper beams that each extends upwardly from an upper end of one of said part-cylinder portions to one of said edges.
 3. The alligator clip described in claim 2 wherein: said bottom beams each has a length that is at least 150% of the length of each of said upper beams.
 4. The alligator clip described in claim 1 wherein: said first piece of sheet metal has an intermediate part lying between said first piece front end and said pin jack, with said intermediate part having a flat bottom that lies in a horizontal plane and side walls that extending upwardly from opposite sides of said flat bottom; said first piece of sheet metal has a predetermined sheet metal thickness; said top edges lie above said horizontal plane and said bottom loop has a bottom that lies below said horizontal plane by a distance (P) that is at least twice the thickness of said sheet metal.
 5. The alligator clip described in claim 1 wherein: said piece of sheet metal has a predetermined thickness and said bottom beams are horizontally spaced apart by a distance that is at least 150% of said sheet metal thickness.
 6. The alligator slip described in claim 1 wherein: said bottom loop extends in a bend of at least 300°.
 7. An alligator clip which includes a first piece of sheet metal with a rear portion bent to form a pin jack that has a horizontal axis and that can receive a cylindrical plug, with said piece of sheet metal having a pair of parallel edges at the top of said rear portion, wherein: said rear portion has a gripping section extending about said axis when viewed in a sectional view taken along said axis, where said gripping section has a bottom part that forms an approximately 360° loop and a pair of primarily parallel bottom beams that extend upwardly from opposite sides of said loop; said gripping section has gripping section opposite sides each bent to engage locations at opposite side portions of said cylindrical plug, said gripping section sides lying at the top of said bottom beams, with said gripping sections sides together forming a region to stably receive said plug and engage.
 8. The alligator clip described in claim 7 wherein: said gripping section has a set of primarily parallel upper beams that extend primarily upwardly from upper ends of said gripping section sides, with said parallel edges lying at the tops of said upper beams.
 9. The alligator clip described in claim 8 wherein: said bottom beams each has a height that is at least 150% the height of each of said upper beams.
 10. The alligator clip described in claim 7 wherein: said first piece of sheet metal has a predetermined thickness; said approximately 360° loop has a sufficient radius that said bottom beams are spaced apart by an average of at least 150% of said thickness.
 11. A method for application to an alligator clip that has a first piece of sheet metal with a rear end having laterally opposite sides and forming a pin jack with a first cylinder which is of a predetermined first diameter, for closely receiving and connecting to a large cylindrical plug of predetermined first diameter, where the method is useful to convert the pin jack so it can closely receive and connect to a second cylindrical plug of a second diameter that is less than said first diameter, wherein said rear end of said first piece of sheet metal has parallel and unjoined edges at a top of said first cylinder, comprising: deforming a bottom portion of said cylinder to laterally compress said bottom portion and thereby form about a 360° loop at the extreme bottom and to leave primarily parallel sides extending upwardly from opposite sides of said loop; deforming said laterally opposite sides of said first cylinder into opposite final sides that lie on horizontally spaced sides of an axis and that engage said second plug and that resist movement of said second plug away from said axis, with said unjoined edges lying above said axis.
 12. The method described in claim 11 including: deforming an upper portion of said first cylinder into two upper beams each extending upwardly from a top of one of said opposite final sides to one of said edges.
 13. The method described in claim 11 wherein: said first piece of sheet metal has a predetermined thickness; said step of deforming a bottom portion of said cylinder includes deforming it to an outside radius of curvature that is at least 150% of the thickness of said sheet metal.
 14. The method described in claim 11 wherein: said first piece of sheet metal has an intermediate portion lying forward of said first cylinder, said intermediate portion having a bottom lying slightly above a bottom of said first cylinder; said step of deforming a bottom portion includes positioning said loop so its bottom lies lower than the bottom of said first cylinder relative to the bottom of said intermediate portion. 